This invention relates to an altitude release mechanism. In more detail, the invention relates to a mechanism for releasing at a predetermined altitude a radiosonde or other instrument package from the balloon carrying it aloft.
A radiosonde is defined in Webster's Unabridged Dictionary as a miniature radio transmitter with instruments that is carried aloft (as by an unmanned balloon) for broadcasting by means of precise tone signals or other suitable method the humidity, temperature and pressure every few seconds. Usually data from as high an altitude as possible are required and the radiosonde is permitted to continue to ascend until the balloon bursts, at which time a parachute will return the radiosonde to the ground.
For investigations extending only to a limited height such as investigations of pollutants within the planetary boundary layer, release of the radiosonde from the balloon at a desired height makes it possible to obtain data on the descent as well as the ascent, provided the altitude of release is picked such that the radiosonde remains in radio range of the receiver on the descent.
Various release mechanisms have been used in the past. For example, two partially evacuated hemispheres which separate at an altitude where ambient pressure equals evacuated pressure have been used. See Angstein et al., Boundary-Layer Meteorology, Vol. 6, pages 129-150 (1974). Disadvantages of this procedure are that air leaking into the system causes premature separation and, alternatively, adhesion between the two hemispheres may cause separation to be delayed.
Another time-release mechanism utilizes an ice cube in which supporting cords are frozen; these separate on thawing. Obviously, this system will not function in freezing weather, is temperature-sensitive and, if the launch is delayed, the separation time will be shortened to include the delay.